You lost muscle because you lost around 1.54% of body weight per week, which is way too aggressive. The maximum recommended amount for losing weight while retaining muscle is around 1%. You will also most likely experience a weight rebound.

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rootusrootus 14 hours ago | parent [-]

Hasn't this mostly been debunked? You lose muscle mass because you lost mass overall, and whether you lost it too quickly or not is not the major factor. AFAIK maintaining muscle mass while losing fat is borderline impossible for anyone who isn't extremely fat and/or very disproportionate composition to begin with.

	▲	olalonde 12 hours ago \| parent [-]
		Not as far as I know. The ratio of fat-to-muscle loss depends on several factors, most notably the rate of weight loss (see https://pubmed.ncbi.nlm.nih.gov/34371981/). In fact, retatrutide is popular notably because it is known to preserve lean body mass better than other weight loss drugs.